Source : Webster's Revised Unabridged Dictionary (1913)

Relapse \Re*lapse"\, n. [For sense 2 cf. F. relaps. See
   {Relapse}, v.]
   1. A sliding or falling back, especially into a former bad
      state, either of body or morals; backsliding; the state of
      having fallen back.

            Alas! from what high hope to what relapse Unlooked
            for are we fallen!                    --Milton.

   2. One who has relapsed, or fallen back, into error; a
      backslider; specifically, one who, after recanting error,
      returns to it again. [Obs.]

Relapse \Re*lapse"\ (r?-l?ps"), v. i. [imp. & p. p. {Relapsed}
   (-l?pst"); p. pr. & vb. n. {Relapsing}.] [L. relapsus, p. p.
   of relabi to slip back, to relapse; pref. re- re- + labi to
   fall, slip, slide. See {Lapse}.]
   1. To slip or slide back, in a literal sense; to turn back.
      [Obs.] --Dryden.

   2. To slide or turn back into a former state or practice; to
      fall back from some condition attained; -- generally in a
      bad sense, as from a state of convalescence or amended
      condition; as, to relapse into a stupor, into vice, or
      into barbarism; -- sometimes in a good sense; as, to
      relapse into slumber after being disturbed.

            That task performed, [preachers] relapse into
            themselves.                           --Cowper.

   3. (Theol.) To fall from Christian faith into paganism,
      heresy, or unbelief; to backslide.

            They enter into the justified state, and so continue
            all along, unless they relapse.       --Waterland.

Source : WordNet®

relapse
     n : a failure to maintain a higher state [syn: {backsliding}, {lapse},
          {lapsing}, {relapsing}, {reversion}, {reverting}]
     v 1: deteriorate in health; "he relapsed" [syn: {get worse}]
          [ant: {get well}]
     2: go back to bad behavior; "Those who recidivate are often
        minor criminals" [syn: {lapse}, {recidivate}, {regress}, {retrogress},
         {fall back}]